But though events such as the increasing anti-Semitism during the summer's Gaza war and the deadly attack on a kosher supermarket in Paris last month have focused the world's attention on the issue, the truth is the Jewish population of Europe has been steadily declining since World War II, as a recent Pew report demonstrates.

The steepest drop, of course, was between 1939 and 1945, when 6 million Jews were killed in the Holocaust and the Jewish population went from 9.5 million to 3.8 million.

But that number has been steadily dropping over the past several decades, especially in Eastern Europe and the former Soviet Union, according to the Pew Research Center's Global Religious Landscape report of 2012 and research by Sergio DellaPergola of the Hebrew University of Jerusalem.

Those data show that in 1960 the Jewish population of Europe dropped to 3.2 million, then to 2 million in 1991, the year the Soviet Union collapsed, and 1.4 million in 2010 – 10 percent of the world's Jewish population and 0.2 percent of Europe's total population.

Expect more to come: The past two years have seen a dramatic rise in Jewish immigration from France, and 2015 looks to be a banner year for the French Jewish exodus.